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Week 1 Genetics > Common genetic disorders > Flashcards

Common genetic disorders Flashcards

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Biology 101 flashcards
1
Q

What are the main clinical features of Huntington’s disease?

A
  • Onset between 30 and 50
  • Progressive chorea, dementia, and psychiatric changes including personality changes and aggression
  • likely underweight due to constant movement and eating/swallowing difficulties
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2
Q

What is the genetic basis of Huntington’s disease?

A
  • AD with genetic anticipation
  • Splice site mutation giving CAG repeat.
  • Shows incomplete penetrance
  • higher chance if dad passes it on
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3
Q

What is the pathogenic mechanism in HD?

A

CAG codes for glutamine, giving a polyglutamine tract which gives insoluble protein aggregates and causes neurotoxicity.

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4
Q

What testing and treatment is available for Huntington’s disease?

A
  • DNA testing for CAG repeat.
  • Children have 50% chance of inheritance, so testing done after discussion and consent
  • No cure
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5
Q

What are the clinical features of myotonic dystrophy?

A
  • Progressive muscle weakness in early adulthood
  • Myotonia and ptosis
  • Cataracts
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6
Q

What is the genetic basis of myotonic dystrophy?

A
  • AD with genetic anticipation
  • CTG repeat in 3’ end of coding region of DMPK gene
  • higher chance if mother passes it on
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7
Q

What is the pathogenic mechanism in myotonic dystrophy?

A
  • Abnormal DMPK mRNA binds to a protein needed for splicing.
  • this has a toxic effect on the splicing of other genes e.g. CLCN1 chloride channel, causing myotonia
  • patients may also have diabetes due to errors in insulin receptor gene
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8
Q

What testing and treatment is available for myotonic dystrophy?

A

No testing is done in children.

No treatment.

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9
Q

What are the clinical features of CF?

A

Recurrent lung infections.
Exocrine pancreatic insufficiency due to thick secretions blocking the pancreatic duct; enzymes can’t get into the digestive system.

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10
Q

What is the genetic basis of CF?

A
  • AR with carrier frequency 1/25 in Caucasians
  • CFTR mutations; most common is F508del- in-frame deletion of phenylalanine prevents normal protein folding.
  • Causes increased thickness of secretions
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11
Q

What testing and treatment is available for CF?

A

Diagnosis can be done by immunoreactive trypsin levels (IRT) in newborns
DNA testing/sweat testing for Cl can be done in childhood, since kids benefit from treatment e.g. breathing aids, nutrition.

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12
Q

What is cascade screening?

A

Screening for mutations in relatives of an affected individual.

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13
Q

What are the clinical features of NF1?

A
  • Cafe au lait macules and neurofibromas
  • macrocephaly
  • learning difficulties in 30%
  • Lische nodules in eyes
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14
Q

What is the genetic basis of NF1?

A
  • Very variable expressivity
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15
Q

What are the complications of NF1?

A
  • Hypertension due to phaeochromocytoma
  • scoliosis
  • tibial fractures
  • sarcomas, optic pathway gliomas
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16
Q

What are the clinical features of DMD?

A
  • Onset 3 years
  • Wheelchair use by 12 years
  • Extreme phenotype
  • Progressive muscle weakness, leading to death
17
Q

What is the genetic basis of DMD?

A
  • Usually an out of frame deletion
  • X linked recessive, so boys are more affected than girls
  • Generate a premature stop codon which results in degeneration of mRNA and no protein production
18
Q

What testing and treatment is available for DMD?

A

Serum creatinine kinase (SCK) levels will be higher in boys from birth due to increased muscle breakdown, before symptomatic.

19
Q

How is BMD different from DMD?

A

Milder phenotype since deletions are more commonly in-frame.
Onset at 11 years and wheelchair use much later in life,

20
Q

What is the genetic basis of fragile X syndrome?

A
  • X linked recessive
  • Shows genetic anticipation
  • Due to upstream repeats in 5’ UTR region (non-coding) of FMR1 gene
21
Q

What are the clinical features of fragile X syndrome?

A

Severe learning disability

22
Q

What is maternal non-disjunction?

A

Failure of the normal separation of 2 chromosomes during the first meiotic division.

23
Q

What’s the difference between balanced and unbalanced chromosomal translocations?

A

Balanced: 2 bits swap e.g. Philadelphia.
Unbalanced: gain an extra bit of a chromosome (can cause miscarriage)

24
Q

What are the key features of Down syndrome?

A

Learning difficulties
Heart malformations
Hypothyroidism
Single palmar crease

25
Q

What are the key features of Patau syndrome?

A 
Congenital heart disease
10% survive first year
Cleft lip and palate 
Microphtlalmia
Abnormal ears
Clenched fists
Post-axial polydactyly
26
Q

What are the key features of Edward’s syndrome?

A

Small chin
Clenched hands and overlapping fingers
Malformations of heart, kidney, other organs.

Week 1 Genetics (5 decks)

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